1. Field of the Invention
This invention relates generally to surgically implanted physiological shunt systems and related flow control devices. More particularly, the present invention relates to a position indicator and adjustment tool for such shunt systems having variable pressure settings for the one-way flow control valves controlling the flow of Cerebral Spinal Fluid (CSF) out of a brain ventricle and preventing backflow of fluid into the brain ventricle.
2. Description of Related Art
A typical adult has a total of about 120-150 cc of CSF with about 40 cc in ventricles in the brain. A typical adult also produces about 400-500 cc/day of CSF, all of which is reabsorbed into the blood stream on a continuous basis.
Sometimes, the brain produces excess CSF. One common cause of the excess production of CSF is hydrocephalus. Hydrocephalus is a condition of excessive accumulation of CSF in the ventricles or brain tissue. Hydrocephalus can result from genetic conditions or from trauma to the brain.
Excessive accumulation of CSF, due to hydrocephalus or other causes, manifests itself as increased pressure within the brain. Whatever the cause, over time, this increased CSF pressure causes damage to the brain tissue. It has been found that relieving the CSF pressure is therapeutically beneficial. This is usually done by draining CSF from the ventricles.
Patients with hydrocephalus often continue to produce excess CSF, at least over some time period. Therefore, it is often desirable to continuously drain excess CSF to maintain normal CSF pressure in the brain. Excessive CSF accumulated in the ventricles of the brain is typically drained away from the brain using a shunt system.
Where hydrocephalus is a chronic condition, the shunt system typically drains the CSF into the patient's peritoneal cavity or into the patient's vascular system. Such shunt systems typically have a catheter implanted in the ventricle of the brain. The catheter is connected to a fluid control device which is in turn connected to a catheter which empties in to the patient's peritoneal cavity or into the patient's vascular system.
An example of a fluid control device is shown in U.S. Pat. No. 5,637,083 issued to William J. Bertrand and David A. Watson on Jun. 10, 1997 entitled “Implantable Adjustable Fluid Flow Control Valve”, the teaching of which is incorporated herein in its entirety by reference. The valve of the '083 patent is shown in FIGS. 1-3 generally labeled 10 (20). (Reference numbers in parentheses correspond to the reference numbers in the '083 patent. After the corresponding reference number to the '083 patent has been given once, no further reference to the '083 will be given although the connection to the '083 patent is intended to be implied throughout this description.) The valve 10 includes a an inlet connector 12 (22) and an outlet connector 14 (24). A elastomeric casing 16 (30) covers the inner workings of the valve 10. A dome 18 (60) extends upward from the elastomeric casing 16. Fluid flows through the valve 10 in the direction indicated by the arrow “A”.
Valve 10 includes a mechanism to control fluid flow through the valve 10. The mechanism includes a magnet 20 (120) embedded within a base 22 (122). Rotating the base 22 changes the internal configuration of the mechanism. Changing the internal configuration of the mechanism produces a variety of pressure or flow characteristics for the valve. The base 22 may be rotated by magnetically coupling an external magnet 24 (140) to the valve's magnet 20 and rotating the external magnet 24. Because magnet 20 is coupled to the external magnet 24, when magnet 24 rotates, magnet 20 also rotates. As magnet 20 rotates, base 22 rotates and the internal configuration of the mechanism changes as described in detail in the '083 patent. As the internal configuration of the valve 10 changes, the pressure/flow characteristics of the valve 10 change.
In use, the valve 10 is subcutaneously placed on the patient's skull. The catheter going to the patient's ventricle in attached to inlet connector 12. The catheter going to the patient's peritoneal cavity or vascular system is attached to outlet connector 14. In this way, a direction of flow is established from the inlet connector 12 through the valve 10 to the outlet connector 14. As stated above and described in detail in the '083 patent, changing the internal configuration of the mechanism by coupling the external magnet to the internal magnet and rotating the base produces a variety of pressure or flow characteristics through the valve 10.
A problem with current adjustable valves, such as the one described in the '083 patent is that once implanted, it is difficult to determine the setting of the valve. Further, it is difficult to adjust the setting of the valve. With some adjustable valves, x-ray images are used to determine the current state or post adjustment state of the valve.